1. Field of the Invention
This invention relates to apparatus and methods for applying liquids to screenprinting screens in, for example, washing operations.
2. Related Background Art
Many operations carried out in the pre-press stages of screenprinting processes involve the application of liquids to frame-mounted screenprinting screens. One such operation is the removal of residual ink from the screen mesh after printing has been carried out. The liquid used for this purpose is typically based on a non-aqueous solvent, in which the residual ink is soluble. Another such operation is the removal of stencil material from the mesh, at the end of the print run for which the stencil was prepared. The liquid used for this operation typically contains periodate or hypochlorite ions as the active agents. The liquids used, in these operations and others, at least after contact with the materials and articles involved, often present either health risks to the operator (making their containment desirable) or cause environmental problems in their disposal. Further, solids typically accumulate in the liquids applied. In the first example, these are sludges derived from the inks; in the second example, the solids are the removed stencil material.
An apparatus for washing-down serigraphical frames is described in U.S. Pat. No. 5,547,567. The apparatus described is however complex and has the disadvantage of including a pump, which needs an external power supply, and switching valves, all of which require maintenance.
U.S. Pat. No. 5,056,948 describes a screen cleaning apparatus which is also complex and includes a scanning spray head and pneumatically powered pumps for removing residue and cleaning fluid.
The present invention seeks to overcome or alleviate these disadvantages.
An object of the invention is accordingly to provide an apparatus and method for applying liquid to a screenprinting screen which does not require any external power or services, including electricity, air and water.
It is a further object to provide such an apparatus which has few moving parts and requires little maintenance.
Another object is to provide such an apparatus which has no electrical parts nor any moving parts liable to produce a spark and therefore gives rise to no significant risk of spark-ignited fire during use.
A further object is to provide such a machine which is constructed of materials which are resistant to a wide range of solvents and other chemicals.
A still further object is to provide such an apparatus which can be used in a recirculation mode, or can be used for single application of liquids.